1. Field of the Invention
This invention relates to shiftable change speed gear devices, preferably multiple countershaft transmissions having resiliently yieldable shifting means for substantially simplifying shifting of the transmissions, utilizing improved blocker and jaw clutch assemblies, and in particular relates to shiftable change speed gear transmissions utilizing an improved blocker means effective to sense only one type of nonsynchronous condition.
2. Background of the Invention
In the design of transmissions, particularly heavy duty transmissions, such as used in trucks, there has existed for a long time the problem of shifting the transmission to the various speed ratios, which problem is even greater when the transmission is provided with an auxiliary transmission section of the range or the splitter type for increasing the number of speed ratios. In most known transmissions, the shifting process is either relatively difficult and/or the shifting mechanism is relatively complex. Thus, there has been a continuing effort in the design of transmissions to improve the shifting, to improve the rapidity of shifting, to reduce the complexity of the shifting mechanism, and to reduce its costs. Hence, without detracting in any way from the operability or desirability of many of the shifting mechanisms previously known, it may be stated that in the present invention these general objectives are accomplished to even a greater degree than has been previously possible.
Particularly, most previously known transmissions have required a relatively high level of operator skill or necessarily utilized synchronizers, or which many different types are known, for causing the speed of the jaw or tooth clutch members to be substantially synchronized prior to permitting their interengagement during a shifting sequence from one speed ratio to another speed ratio. While the use of synchronizers does permit the shifting operation to be performed, their use, as is already known, imposes certain requirements of weight, space and power which is desirable to ease, or avoid entirely, if possible.
These and other problems incident to previously known transmissions were set forth and acknowledged in U.S. Pat. Nos. 3,799,002, entitled "TRANSMISSION WITH RESILIENTLY LOADED MAIN SHAFT GEARS"; 3,910,131, entitled "TRANSMISSION WITH SNAP SHIFT"; 3,921,469, entitled "TRANSMISSION WITH RESILIENTLY LOADED MAIN SHAFT GEARS"; 3,924,484, entitled "SENSOR UNBLOCKING RAMPS"; and 3,983,979, entitled "SENSOR UNBLOCKING RAMPS"; all hereby incorporated by reference and all issued to the present applicant and assigned to the same assignee as the present application. Apparatus was disclosed in the above mentioned patents which effectively meets the problems while providing a reliable, effective and efficient transmission, particularly for heavy duty use.
While both forms of the inventions disclosed in said patents, namely, those using blockers and those not using blockers, are effective for carrying out the objectives thereof, it has been noted that for the usual reasons both noise and clutch tooth wear can be minimized by the use of blockers as set forth in said patents and since the date thereof a considerable amount of investigation has been carried out related thereto, both for simplifying of the blocker structure and for improving the operation of said blockers and of transmissions utilizing same. Blockers of various types are well known in the prior art and examples thereof may be seen by reference to the above mentioned patents and to U.S. Pat. No. 3,503,280, entitled, "BLOCKER DEVICE", issued to W. C. Bopp, and assigned to the assignee of this application.
Blockers of the type illustrated in the above mentioned patents are generally nondeformable devices designed to prevent, or block, the engagement of the axially engageable jaw clutch members of a jaw clutch when said members are rotating at substantially different speeds, i.e., are not substantially synchronized. Transmissions utilizing such blockers are referred to as "blocked transmissions". Such blockers are generally retained on one clutch member for rotation therewith with a limited amount of relative rotation (typically 3.degree.-15.degree.) provided. The blocker and the one clutch member will define an array of projections or the like which will allow the one clutch member to move relatively axially towards the other clutch member when in alignment but will block such relative axial movement when said blocker is rotated in either the clockwise or counterclockwise direction relative to the one clutch member. The blocker is designed to be in frictional contact with the second clutch member during an engaging operation as will thus tend to rotate with the second clutch member.
By way of example, assuming the use of a blocker as disclosed in the prior art and that the clutch members are rotating in a clockwise direction, if the first clutch member is rotating faster than the second clutch member, upon initiation of an engaging operation the blocker will be rotated counterclockwise relative to the first clutch member and the blocker will prevent axial movement of the first clutch member towards the second clutch member. If the second clutch member is rotating faster than the first clutch member, the blocker will be rotated clockwise relative to the first clutch member and the blocker will prevent axial movement of the first clutch member towards the second clutch member. If the first clutch member initially rotated faster, then slower than the second clutch member, the blocker would, relative to the first clutch member, rotate in a clockwise direction from an initial counterclockwise rotated position relative to the first clutch member towards a relatively clockwise rotated position. During the relative rotation, for at least a limited period of time, the blocker would align with the first clutch member and cease to block axial movement thereof toward the second clutch member. Such movement of the blocker is generally referred to as "passing through synchronous". The clutch will "pass through synchronous" or "cross synchronous" as the two clutch members reach a substantially synchronous rotation, and the clutch engaging operation, or the gear shift, should be completed at this time. As the blocker is designed to be in constant frictional contact with the second clutch member only during a clutch engaging operation to prevent undue frictional wear, it was possible, under certain conditions, that the blocker would be set up on the "wrong side of synchronous" at the initiation of a clutch engaging operation, i.e., rotated clockwise relative to the first clutch member when the first clutch member was rotating faster than the second clutch member or vice versa. Under such conditions, especially with the vehicle stopped, it was difficult and/or impossible to cause the blocker to "pass through synchronous" and thus difficult and/or impossible to cause the transmission to be shifted into the desired gear ratio.
For those somewhat unusual operating conditions when the blocker would be improperly positioned relative to the first clutch members, the required shift (clutch engagement) could occur if a self-aligning mechanism was provided to align the blocker with the first jaw clutch member or if the blocker was caused to set up on the opposite side of synchronous such as by a momentary reversing of the main shaft. Such a momentary reversing could usually be obtained by momentarily shifting from neutral into reverse. But this was obviously an inconvenience, a highly undesirable technique, and might hamper the commercial acceptability of an otherwise highly successful transmission. Self-aligning mechanisms are usually effective but involve rather complicated structure and usually must be utilized in connection with an input shaft brake. One method of minimizing or eliminating this problem involved the use of the structures illustrated in U.S. Pat. No. 3,924,484 and 3,983,979, mentioned above and incorporated by reference. While this method has proven highly effective, an improvement appeared obtainable as to the positive clutch and blocker assembly associated with at least the low-speed gears.